Electrospinning apparatus and method for producing fiber assembly

ABSTRACT

An electrospinning apparatus for depositing fibers on a target having first and second surfaces opposed to each other. The apparatus includes a discharger that discharges a material solution of the fibers towards the first surface of the target, a collector electrode containing a top portion opposed to the discharger, a holder that holds the target between the discharger and the collector electrode so that the first surface of the target is opposed to the discharger, a power supply, a shift regulator that shifts the holder in a direction parallel to the first surface of the target, a distance regulator that regulates a target distance between the top portion of the collector electrode and the second surface of the target, and a controller that controls the shift regulator and the distance regulator to produce a fiber assembly having a given deposited condition on the first surface of the target.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority under 35 U.S.C. § 119 with respect to the Japanese Patent Application No. 2018-055119, filed on Mar. 22, 2018, of which entire content is incorporated herein by reference into the present application.

TECHNICAL FIELD

The present invention relates to an electrospinning apparatus and a method for producing a fiber assembly.

BACKGROUND

In an electrospinning method using an electrospinning apparatus, a nozzle for discharging or extruding a material solution containing a fiber material dissolved therein is applied with a voltage relative to a collector electrode on which a target is set, to electrically charge the material solution and the target of polarity different from each other. After the material solution is discharged from the nozzle to the target, it is subjected to an electrostatic explosion, so that the fiber material is isolated from the material solution. The isolated fiber material is electrostatically drawn by the collector electrode and is deposited thereon as a fiber assembly.

Patent Document 1 (JP 2013-019073 A) discloses a collector electrode configured to be shifted in a direction parallel to a surface of the target for evenly depositing the fiber on the target.

The electrospinning method may be used to produce a thin fiber having a diameter of nano-meter size (so-called a nanofiber). As applications of the nanofiber are expanded, a demand is increased for a technique to control a pattern of the fibers deposited on the target as desired.

SUMMARY

One aspect of the present invention relates to an electrospinning apparatus for depositing fibers on a target having first and second surfaces opposed to each other, the electrospinning apparatus comprises a discharger that discharges a material solution of the fibers towards the first surface of the target, a collector electrode containing a base portion and a top portion opposed to the discharger, a holder that holds the target between the discharger and the collector electrode so that the first surface of the target is opposed to the discharger, a power supply that applies a voltage between the discharger and the collector electrode, a shift regulator that shifts the holder in a direction parallel to the first surface of the target, a distance regulator that regulates a target distance between the top portion of the collector electrode and the second surface of the target, and a controller that controls the shift regulator and the distance regulator to produce a fiber assembly having a given deposited condition on the first surface of the target.

Another aspect of the present invention relates to a method for producing a fiber assembly, which comprises steps of, preparing a material solution containing a raw material of fibers, preparing a target having first and second surfaces opposed to each other, holding the target between a discharger and a collector electrode so that the first surface of the target is opposed to the discharger, the collector electrode containing a base portion and a top portion opposed to the discharger, electrospinning a fiber to form a fiber assembly having a given deposited condition on the first surface of the target by i) applying a voltage between the discharger and the collector electrode, ii) discharging the material solution of the fibers towards the first surface of the target, iii) shifting the target in a direction parallel to the first surface thereof, and iv) regulating a target distance between the top portion of the collector electrode and the second surface of the target.

While the novel features of the invention are set forth particularly in the appended claims, the invention will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the electrospinning apparatus according to one embodiment of the present invention, schematically illustrating a structure thereof.

FIG. 2 is a block diagram of the electrospinning apparatus according to the embodiment of the present invention.

FIG. 3 is a perspective view of the electrospinning apparatus of FIG. 1.

FIG. 4 is a top plan view of a collector electrode of the electrospinning apparatus of FIG. 1, showing a top portion thereof.

FIG. 5A is a side view partially showing the collector electrode of FIG. 3.

FIGS. 5B-5G are perspective views partially showing the collector electrode according to further embodiments of the present invention.

FIG. 6 is a cross-sectional view of an example of the discharger according to one embodiment of the present invention.

FIG. 7 is a photograph of a fiber assembly produced by the electrospinning apparatus with a method for producing the fiber assembly according to the present invention.

DETAILED DESCRIPTION

In an electrospinning method, a material solution is discharged from a nozzle (referred to as a discharger herein) subjected to an electrostatic burst or explosion, thereby to produce a thin fiber which spreads across a hemispherically region with a center of the nozzle tip. This makes it difficult to deposit the fiber in a particular area or position on a target. If the target is made of non-conducting material, as the electrospinning method continues, electrical charges are accumulated thereon, of which polarity is same as one of the fibers, which may in turn change an electric field in an electrospinning space with the fibers deposited on the target so that the fiber further extruded from the nozzle is deposited on the target in an unintentional area or position. Thus, it is difficult to control the deposited area or position of the fibers as expected.

In the present embodiment, a collector electrode is used, which has a column portion and a top portion at a top end thereof. The fiber produced in the electrospinning space is drawn to the target (referred to also as a base member) at the position near the top portion of the collector electrode. This allows the fibers to be deposited in a selected or limited area or position on the target. Also, translation or shift of the target along a plane parallel thereto allows the fibers to be deposited along a desired contour or shape corresponding to a translation track of the top portion relative to the target. Furthermore, in the present embodiment, a deposited condition of the fibers is controlled by changing a distance between the top portion and the target. In the present disclosure, the deposited condition intends, for example, a deposited amount and a deposited area or pattern of the fibers. As such, a fiber assembly having a desired deposited pattern can be formed on the target.

With reference to the attached drawings, an electrospinning apparatus according to the present embodiment will be described hereinafter. FIG. 1 is a side view of an electrospinning apparatus according to one embodiment of the present invention illustrating schematic structure thereof. FIG. 2 is a block diagram of the electrospinning apparatus according to the embodiment. FIG. 3 is a perspective view of the electrospinning apparatus of FIG. 1. FIG. 4 is a top plan view of a collector electrode, showing a top portion thereof. FIG. 5A is a side view partially showing the collector electrode. FIGS. 5B-5G are perspective views partially showing the collector electrode. In the description of the present embodiment, a couple of terms for indicating the directions (for example, “X-”, “Y-”, “Z-”) are conveniently used just for facilitating clear understandings, it should not be interpreted that those terms limit the scope of the present invention. Also, in the drawings, the target is illustrated in a rectangular form, but the shape of the target is not limited thereto. In FIG. 3, the deposited fibers (the fiber assembly) are conveniently illustrated with pale lines.

As illustrated in FIG. 1, the electrospinning apparatus 10 includes a discharger 1 (nozzle) which is adapted to discharge a material solution of the fibers, a collector electrode 2 which is arranged opposed to the discharger 1 and includes a base portion 2B and a top portion 2T, a holder 3 (e.g., a holding frame) which is adapted to hold a target 20 that receives the fibers discharged from the discharger 1 thereon. The base portion 2B is in a column shape. The top portion 2T is arranged at the tip of the base portion 2B opposed to the discharger 1. The holder 3 is configured to hold the target 20 between the discharger 1 and the top portion 2T so that a first surface 20X of the target 20 faces upward to the discharger 1.

As illustrated in FIG. 2, the electrospinning apparatus 10 also includes a controller 11 configured to control a power supply 12, a shift regulator 13, and a distance regulator 14 each connected thereto. The power supply 12 is adapted to apply a given voltage between the discharger 1 and the collector electrode 2. The shift regulator 13 is adapted to translate or shift the holder 3 along a plane parallel to the first surface 20X. The distance regulator 14 is adapted to change or regulate a distance “A” (denoted in FIG. 1) between the top portion 2T and a second surface 20Y of the target 20 held by the holder 3 so as to control a deposited condition of the fibers in the first surface 20X. The collector electrode 2 may be grounded, but preferably applied with a voltage of a polarity opposite to the discharger 1 by means of the power supply 12 so as to improve the accuracy of the deposited pattern of the fibers.

Furthermore, the electrospinning apparatus 10 may include a Human/Machine Interface (HMI) 15, a deposited-condition detector (referred to also as a first detector) 16, and a distance detector 17 (referred to also as a second detector), each of which is connected to the controller 11. The HMI 15 allows an operator to design and input the deposited pattern of the fibers on the target. The deposited-condition detector 16 is adapted to monitor and feedback the deposited condition to the controller 11, and the distance detector 17 is also adapted to monitor the distance A between the top portion 2T and the target 20 and feedback the monitor distance A to the controller, as will be described later.

The material solution discharged from the discharger 1 is drawn to the collector electrode 2 that is electrically charged with the polarity different from the discharger 1. In the electrospinning apparatus 10, the target 20 is typically arranged close to the collector electrode 2, in order to define a sufficient space (referred to as an electrospinning space herein) for electrostatic explosion and electrostatic extension, thereby to reliably deposit the fibers on the target 20. The distance between the target 20 and the collector electrode 2 gives a great impact on deposit efficiency of the fibers on the target 20.

In this embodiment, the collector electrode 2 is provided with the base portion 2B having a column shape and the top portion 2T, and the distance A between the top portion 2T and the second surface 20Y of the target 20 held on the holder 3 is regulated by the distance regulator 14 in conjunction with the controller 11 so as to deposit the fibers at the limited area on the target 20.

Thus, the amount (mass per unit area) and/or the area of the fibers deposited on the first surface 20X of the target 20 can be regulated in accordance with the distance A. When the distance A exceeds a threshold A₀, the fibers may drift in the electrospinning space and adhere to a peripheral component of the electrospinning apparatus 10 without being deposited on the target 20. When the distance A is not greater than the threshold A₀, the fibers are at least partially drawn to the top portion 2T of the collector electrode 2 and deposited on the limited area of the target 20. Also, when the distance A is not greater than the threshold A₀, as the distance A is smaller, the area where the fibers are deposited is smaller. That is, even if the material solution is kept discharged at a given rate, the amount and the discrete/continuous area of the fibers deposited on the target 20 can be regulated or controlled. As shown in FIG. 3, the fibers can be deposited on the area along the desired contour corresponding to the translation track of the top portion relative to the target 20 by translation or shift of the target in the plane (XY-plane) parallel to the target 20. This is achieved by the shift regulator 13 (not shown in FIG. 3) which shifts the X- and Y-positions of the target 20 relative to the collector electrode 2, so that the desired deposited pattern of the fibers can be formed on the target 20. Alternatively, the shift regulator 13 may shift the X- and Y-positions of the collector electrode 2 together with the discharger 1 relative to the target 20.

In the electrospinning method, at the beginning when the material solution is initiated to be discharged, the electric field in the electrospinning space is unstable, which in turn likely produces the fibers in a less homogeneous manner. However, according to the present embodiment, while the material solution is kept discharged, the desired deposited pattern can be formed to obtain a fiber assembly of a high quality.

As above, the threshold A₀ is defined as the maximum distance between the top portion 2T and the second surface 20Y of the target 20, which allows the discharged fiber to be deposited on the target 20. The threshold A₀ may be selected in accordance with parameters including, for example, the distance between the discharger 1 and the top portion 2T of the collector electrode 2, the voltage applied therebetween, the material of the target 20 and the holder 3, and the electric potential of the collector electrode 2. The threshold A₀ may be, for example, in a range between 0.5 mm and 2 mm.

FIG. 1 denotes the distance A as the closest distance between the top portion 2T and the second surface 20Y of the target 20. The distance A may be greater than the threshold A₀ in a case or less in another case. The distance A may be even zero, in which, in other words, the top portion 2T may contact with the second surface 20Y of the target 20. The distance A may be, for example, in a range between 0 mm and 3 mm.

The target 20 may slightly be pushed upward by the top portion 2T. The maximum distance in a Z-direction between the portion of the target 20 pushed up by the top portion 2T and another portion thereof may be, for example, in a range between 0 mm and 2 mm. The Z-direction is one normal or perpendicular to the direction parallel to the first surface 20X (XY-plane) of the target 20.

The shape of the holder 3 is not specifically limited as long as it can hold the target 20 without having it loosened. The target 20 is held by the holder 3 to keep especially a deposition region 20 a (a region where the first surface 20X of the target 20 is uncovered by the holder 3 and the fibers can be deposited) to be unloosened. When the deposition region 20 a is surrounded by a non-deposition region 20 b where no deposited pattern of the fibers can be formed, the holder 3 preferably holds at least a part of the non-deposition region 20 b on the first surface 20X and/or a region on the second surface 20Y corresponding to the non-deposition region 20 b. This structure can readily reduce the distance A between the second surface 20Y and the top portion 2T, and for instance, may allow the top portion 2T in contact with the second surface 20Y of the target 20.

When the target 20 has a peripheral portion, the holder 3 may include a frame body holding the peripheral portion of the target 20, as shown in FIG. 3. In order to facilitate handling and storing the holder 3, it may be shaped of a rectangular annular body as shown in FIG. 3. Also, in order to facilitate maintaining a uniform distribution of the electric field and forming the fiber in a stable manner during the electrospinning process, the holder 3 may be formed of a circular annular body. The holder 3 may have a three-dimensional structure, an entire of which is not arranged on the same plane. Alternatively, the holder 3 may have a handle at a position being not in contact with the target 20, and may have a non-opposed portion which is not opposed to the target 20.

The material of the holder 3 is not specifically limited and may be appropriately selected in accordance with various factors including, for example, an application for the electrospinning process, a withstanding voltage applied in the electrospinning process, a solvent-proof characteristic against a solvent contained in the material solution, a mechanical strength, and the electrostatic property. Especially when taking consideration of the application for the electrospinning process, the holder 3 is preferably made of insulating material.

The holder 3 is bonded to the target 20, for example, using an adhesive. The holder 3 may hold the target 20 either on the first surface 20X, the second surface 20Y, or both of them.

If the target 20 has an insufficient mechanical strength, a protection member (not shown) for protecting the target 20 from an external force may be provided between the second surface 20Y and the top portion 2T. The protection member is preferably thin having the thickness of, for example, at least 0.01 mm and no greater than 0.2 mm. When the thickness of the protection material is within this range, the protection member can suppress the damage of the target 20 without disturbing the deposition of fibers on the desired positions or area. The protection material is not specifically limited and may be formed of the material in the configuration same as the target, as will be described later. The protection material may be formed of, for example, an insulating film and a non-woven fabric.

The collector electrode 2 includes at least the base portion 2B and the top portion 2T, and may consist of the base portion 2B and the top portion 2T. Also, the collector electrode 2 may further have a plate electrode (not shown), on which the base portion 2B and the top portion 2T are arranged. The base portion 2B may be formed integrally with or separately from the top portion 2T.

The base portion 2B is in a column configuration which includes, for example, a rod-shape, a pin-shape, and a pen-shape. The base portion 2B has a cross-sectional view taken along the plane parallel to the first surface 20X, which although not limited thereto, may include a circular, elliptical, rectangular or another polygonal shape. The base portion 2B may have a rotation axis extending therethrough along a direction perpendicular to the first surface 20X and be configured to be rotatable around the rotation axis.

The top portion 2T is positioned at the end of the base portion 2B opposing to the second surface 20Y. The top portion 2T has a top or projected shape viewed from a direction perpendicular to the first surface 20X, and may be in a circular (as shown in FIG. 4), elliptical, rectangular, polygonal, or an irregular undefined shape, although not specifically limited thereto. The projected shape of the top portion 2T has a size or area, which is not specifically limited and may be determined in accordance with the deposited pattern, for example. The size or area of the projected shape of the top portion 2T may be, for example, in a range between 1/50 and 1/200 of that of the first surface 20X.

The entire configuration of the top portion 2T is not specifically limited and may be formed in a hemispherical, cone, pyramidal, columnar, prismatic, arc columnar or T-shape, or formed in a shape corresponding to the deposited area, or combinations any one of those shapes (See FIGS. 5A-5G). FIGS. 5A-5G each illustrate the base portion 2B in a columnar configuration.

FIG. 5A illustrates the collector electrode 2A having the top portion 2Ta in a hemispherical shape. The hemispherical top portion 2Ta is preferable because of no sharp edge. The sharp edge of the top portion 2T likely draws an intensive electric field thereon, which may deteriorate the accuracy in formation of the deposited pattern of the fiber assembly on the target 20. Also, the sharp edge of the top portion 2T likely damages the target 20 and/or prevents it from being shifted or translated, especially when the top portion 2T contacts with the second surface 20Y of the target 20.

In FIG. 5A, the top portion 2Ta has a curvature radius same as the base portion 2Ba, although not limited thereto. The curvature radius of the top portion 2Ta may be smaller or larger than the radius of the columnar base portion 2Ba.

The top portion 2Tb of the collector electrode 2B shown in FIG. 5B is in a shape of a column. The collector electrode 2B with the columnar top portion 2Tb promotes the deposited pattern having a relatively thick line. In FIG. 5B, the top portion 2Tb has a diameter larger than the base portion 2Bb, although not limited thereto. The diameter of the top portion 2Tb may be the same as or smaller than that of the base portion 2Bb. A hemispherical or conical projection may be provided about the center of the top portion 2Tb. The top portion 2Tb may be in a shape of a prism, instead of the column. The longest side of the prismatic top portion 2Tb may be larger or smaller than the diameter of the columnar base portion 2Bb. The smallest side of the prismatic top portion 2Tb may be larger or smaller than the diameter of the columnar base portion 2Bb.

The top portion 2Tc of the collector electrode 2C shown in FIG. 5C is shaped in a cone. The collector electrode 2C with the columnar top portion 2Tc promotes the deposited pattern having a thin line. In FIG. 5C, the bottom surface of the top portion 2Tc has a diameter same as that of the base portion 2Bc, although not limited thereto. The diameter of the bottom surface of the top portion 2Tc may be smaller or larger than that of the base portion 2Bc. Furthermore, the top portion 2Tc may be provided at the tip thereof with a ball-shaped or ring-shaped member, so that the target 20 can be smoothly shifted or translated by the shift regulator 13.

The top portion 2Td of the collector electrode 2D shown in FIG. 5D is designed to have a shape corresponding to the area with the fiber assembly deposited. FIG. 5D shows a ring-shaped top portion 2Td, for example. The desired deposited pattern can readily be formed by means of the top portion 2Td having the shape corresponding to the deposited area.

The top portion 2Te of the collector electrode 2E shown in FIG. 5E includes an arc part and a column part for connection with the base portion 2Be, which is thus T-shaped. The arc part has two of arc sides with an interior angle of 90 degrees and a quarter-circular ridge between the sides. The ridge of the arc part is designed to oppose to the target 20 and has a width which is gradually narrower as closer to the target 20, which continuously change the distance to the target 20 as well as the area opposing thereto. The top portion 2Te so structured achieves a simple way to produce the fiber assembly having a gradation in the deposited pattern. The interior angle of the arc part is not limited to 90 degrees and may be, for example, in a range between 45 degrees and 180 degrees.

The top portion 2Tf of the collector electrode 2F shown in FIG. 5F includes a prismatic column 22Tf and two cones 21Tf extending therefrom. The prismatic column 22Tf is a seat for supporting the cones 21Tf. The prismatic column 22Tf is connected to the cones 21Tf. The collector electrode 2F may include three or more cones 21Tf, which achieves the deposited pattern having a plurality of thin lines in an efficient manner.

When the base portion 2Bf is rotatable, two cones 21Tf may be arranged so that centers thereof are offset by different distances to a rotation axis of the base portion 2Bf, which readily achieves the deposited pattern having a plurality of concentric arcs or circles. The top portion 2Tf may have only one cone 21Tf of which center is offset to the rotation axis of the base portion 2Bf, which also efficiently achieves the deposited pattern in an arc shape.

The top portion 2Tg of the collector electrode 2G shown in FIG. 5G includes a cone 21Tg and an insulating ring 23Tg surrounding thereof. The ring 23Tg can be a guide defining a distance between the second surface 20Y and the tip of the cone 21Tg, which in turn achieves deposited pattern in a reliable manner. The cone 21Tg and the ring 23Tg each are connected to the base portion 2Bg. The ring 23Tg may be connected to the base portion 2Bg slidably in the Z direction. Moreover, a conducting ring (not shown) larger than the ring 23Tg may be arranged concentrically with the ring 23Tg. The conducting ring is connected to a ground level to change the potential relative to the cone 21Tg and to draw the fibers towards the cone 21Tg, which facilitates the formation of the desired deposited pattern in a more efficient manner.

Besides, although not illustrated, the top portion 2T may include a parabolic dish member having a diameter much (three times or more) larger than the diameter of the base portion 2B and a cone arranged at the center thereof. The parabolic dish member is arranged so that the concave surface thereof is opposed to the target 20, which establishes a stable electric field between the parabolic dish member and the discharger 1, so as to precisely control the deposited positions or area of the fibers. Instead of the parabolic dish member, the columnar top portion 2T having a diameter much larger than that of the base portion 2B may be adapted. The top portion 2T shaped as the parabolic dish member or the column may be provided at the center thereof with a hemisphere member instead of the cone.

The fibers are deposited on the first surface 20X in the area substantially corresponding to the projected shape of the top portion 2T, which is referred to as the deposited area herein. When the top portion 2T is shaped, for example, in a hemisphere having the curvature radius of 5 mm and the top portion 2T contacts with the second surface 20Y (A=0), the fibers are accumulated in the deposited area of a circle having a diameter in a range between 2.5 mm and 3 mm. When the protection material is provided between the second surface 20Y and the top portion 2T, or when the top portion 2T has no contact with the second surface 20Y (0<A≤A₀), the diameter of the deposited area may slightly be larger than 3 mm.

The whole collector electrode 2, the base portion 2B, or the top portion 2T may be connected to the distance regulator 14 in a detachable or replaceable manner, so that a variety of deposited patterns are formed on the target 20, by using one or more top portion 2T having different projected shapes in size and configuration.

In a preferred embodiment, the distance regulator 14 is adapted to regulate the distance A between the second surface 20Y of the target 20 and the top portion 2T by moving upward or downward the collector electrode 2 (rather than the discharger 1). Since the distance A between the discharger 1 and the target 20 is maintained unchanged according to the present embodiment, the electric field in the electrospinning space can be kept stable, thereby to realize the reliable electrospinning process. In this case, the distance regulator 14 includes a first elevator (not shown) for moving the collector electrode 2, which is electrically isolated or insulated from the collector electrode 2, in order to precisely regulate the positions thereof.

Alternatively, the distance regulator 14 may include a second elevator (not shown) for moving the holder 3 upward or downward, thereby to change the distance A between the collector electrode 2 and the target 20. When the holder 3 is formed of an insulating material, the second elevator is not required to be formed of an insulating material for electrically isolating or insulating it from the holder 3, which advantageously simplifies the structure of the distance regulator 14 or the second elevator.

With the material solution being discharged from the discharger 1, especially when the given condition (A<A₀) is met to allow the fibers deposited on the target 20, the direction (the first direction) extending from the discharger 1 to the tip of the top portion 2T closest to the second surface 20Y is preferably kept unchanged. Thus, the distance regulator 14 is preferably configured to maintain the first direction unchanged, while regulating the distance A between the collector electrode 2 and the target 20. Even if the shift regulator 13 shifts or translates both of the discharger 1 and the collector electrode 2 relative to the target 20, the X- and Y-positions thereof are kept unchanged relative to each other, which steadies the direction (first direction) along which the fiber is drawn so as to facilitate electrospinning the fiber in a stable manner and depositing the fiber assembly at the desired positions on the target 20.

Especially, while the given condition (A<A₀) is met to allow the fibers deposited on the target 20, it is preferable to shift or translate only the target 20 along the plane parallel to the target 20, e.g., in the XY-direction, with the discharger 1 and the collector electrode 2 being kept stationary. In other words, the shift regulator 13 is configured to shift or translate the target 20 in directions parallel to the XY-plane preferably without changing the position thereof in the Z-direction. The shift regulator 13 so structured also contributes to keep the distance A and the first direction unchanged, thereby to facilitate electrospinning the homogeneous fibers and depositing the fiber assembly with the desired pattern in a more accurate manner.

The shift regulator 13 is also configured to regulate the deposited area, the deposited pattern, and/or the deposited amount of the fibers by selecting or optimizing a number, direction, and rate for translating the target 20 in the XY-direction. For example, the shift regulator 13 may translate the target 20 along a given translation track several times each having a small deviation from the previous one, so that the deposited pattern has a width greater than the size of the projected shape of the top portions 2T and/or the deposited pattern has a gradation along the translation track. Also, the shift regulator 13 may translate the target 20 repeatedly along the same translation track, so that the deposited pattern has a greater thickness in the Z-direction (e.g., FIG. 3), thereby to increase the mass of fibers in a unit area.

The amount of the fibers deposited on the target 20 may also be regulated by elevating the collector electrode 2 or the holder 3 for changing the distance A using the first or second elevator (the distance regulator 14). The amount of the deposited fibers may further be adjusted by changing the voltage between the discharger 1 and the collector electrode 2 by the power supply 12, the volume of the material solution discharged from the discharger 1, or the potential of the target 20 or the holder 3. Especially for electrospinning the homogeneous fiber, the amount of the deposited fibers may preferably be controlled by changing the translation rate of the target 20 in the XY direction or the distance A between the collector electrode 2 and the target 20.

The first direction extending from the discharger 1 to the tip of the top portion 2T closest to the second surface 20Y is not specifically limited to the Z-direction perpendicular to the first surface 20X, and may be inclined to the Z-direction at an acute angle of 20 degrees or less, taking into consideration of the stability of the electrospinning and the accuracy of the deposited pattern. In the present disclosure, the first direction may be described as being constant even when the first direction varies within 10 degrees from the targeted direction, and also the distance A may be described as being constant even when the distance A varies within 10% from the targeted distance A.

The electrospinning apparatus 10 may further include the deposited-condition detector 16 (first detector) adapted to detect the deposited condition such as the deposited area and the amount of the fibers deposited on the first surface 20X. The data of the deposited area and the deposited amount which are obtained by the first detector may be fed back to the controller 11 which is configured to control the shift regulator 13 and the distance regulator 14, to determine or optimize the operation parameters including, for example, the volume of the material solution discharged from the discharger 1, the motions/shifts and the directions of the collector electrode 2 and the holder 3. Alternatively, the desired pattern and amount of the fibers to be deposited on the target 20 may be predetermined by inputting data to the controller through the HMI 15 so that it controls the shift regulator 13 and the distance regulator 14 to deposit the fibers in the desired pattern and amount on the target 20.

As the fibers are kept deposited on the target 20, the electric charges of the polarity same as the fibers are accumulated on the target 20 which likely has the potential closer to the discharger 1 (the material solution). This attracts the target 20 with a greater force to the top portion 2T having the potential of the polarity opposite to the fibers, which in turn interferes in the control of the distance A. As such, the electrospinning apparatus 10 may further include the distance detector 17 (second detector) adapted to detect the distance A between the second surface 20Y and the top portion 2T. The data of the distance A obtained by the distance detector 17 may be fed back to the controller 11 to drive the distance regulator 14 so as to adjust or optimize the distance A. Furthermore, the electrospinning apparatus 10 may include a static remover (not shown) for removing the static charges accumulated on the target 20. The static remover may be configured to have any appropriate structures, which may be, for example, a static removing brush, an air ionizing blower (in conjunction with a corona discharge device) for blowing a wind containing ions to the target 20, and an ionizing radiator for radiating an ionizing radiation such as an ultra-violet beam on the target 20. The air ionizing blower is preferably used for removing the static charge on the target 20, which more likely suppress a damage of the fibers (fiber assembly) deposited on the target 20.

The discharger 1 is formed of a conducting material in a cylindrical shape with a hollow space (not shown) therein. The material solution to be discharged is received within the hollow space. The discharger 1 is provided with at least one discharging outlet 1 a for discharging the material solution, which opposes to the target 20. The discharging outlet 1 a may be arranged away from the target 20 at a distance in a range between 100 mm and 600 mm, depending upon the scale of the electrospinning apparatus 10 and the diameter of the fibers to be deposited. The material solution received within the hollow space of the discharger 1 is discharged from the discharging outlet 1 a toward the target 20 by means of a pump (not shown) in a fluid communication with the hollow space. The aforementioned structure of the discharger 1 is exemplary and not limited thereto.

The discharger 1 shown in FIG. 6 defines an inside chamber and includes a conduit extending therethrough to the discharging outlet 1 a, which defines a first flow channel 1A for guiding the material solution. The discharger 1 also defines a second flow channel 1B along with the inside chamber for guiding a gas. In the inside chamber, the material solution through the first flow channel 1A is isolated from the gas through the second flow channel 1B. The first discharging outlet 1 a is provided for discharging the material solution 30 at the end of the conduit opposed to the target 20. The second discharging outlet 1 b is provided for discharging the gas at the end of the discharger 1 also opposed to the target 20. The second discharging outlet 1 b is arranged so as to surround a periphery of the first flow channel 1A or the first discharging outlet 1 a. The discharger 1 is designed so that the material solution 30 is discharged from the first discharging outlet 1 a to the electrospinning space with the surrounding gas from the second discharging outlet 1 b. This suppresses the expansion of the electrostatic explosion of the fiber during the electrospinning process, thereby to improve the accuracy of the deposited position or pattern of the fibers.

The voltage or the electric field between the discharger 1 and the collector electrode 2 may produce reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) from oxygen and/or nitrogen in the atmosphere or the electrospinning space. However, the material solution 30 discharged into electrospinning space can be protected from ROS and RNS by the gas discharged from the second discharging outlet 1 b. Furthermore, the gas around the material solution 30 is less charged so as to achieve electrospinning the fiber in a more reliable manner.

As shown in FIG. 6, the end of the first discharging outlet 1 a of the first flow channel 1A is positioned preferably closer to the target 20 than the second discharging outlet 1 b of the second flow channel 1B. The gas flow from the second discharging outlet 1 b to the electrospinning space further suppresses the expansion of the electrostatic explosion of the fiber. In addition, a point where the electrostatic explosion of the material solution 30 is initiated gets closer to the target 20, thereby to further improve the accuracy of the deposited position or pattern of the fibers.

Although not specifically limited thereto, the flow rate of the gas may be, for example, between 1 l/min. (liter/minute) and 15 l/min. and preferably between 5l/min. and 10 l/min. The expansion of the electrostatic explosion can be suppressed or controlled by keeping the flow rate of the gas within this range. Although not specifically limited thereto, the gas may be dry air or nitrogen gas, for example, which gives no impact on the fiber discharged from the discharger 1.

The electrospinning apparatus 10 may comprise a plurality of dischargers 1, in which one or more of the dischargers 1 may be selectively activated in accordance with the desirable deposited pattern of the fiber assembly.

The electrospinning apparatus 10 may further include a sucking mechanism or a vacuum mechanism for removing unnecessary fibers from the electrospinning space. The unnecessary fibers are intended as the fibers which possibly drifts in the electrospinning space without reaching to the target 20. The electrospinning apparatus 10 may also include a cleaning mechanism adapted for cleaning the discharger 1, especially the discharging outlets thereof. Although not specifically illustrated, the sucking/vacuum mechanism and cleaning mechanism may be controlled by the controller 11.

Next, a method for producing the fiber assembly of the present embodiment will be described hereinafter. The method for producing the fiber assembly comprises steps of preparing a material solution containing a raw material of fibers, preparing a target having first and second surfaces opposed to each other, holding the target between a discharger and a collector electrode so that the first surface of the target is opposed to the discharger, the collector electrode containing a base portion and a top portion opposed to the discharger, electrospinning a fiber to form a fiber assembly having a given deposited condition on the first surface of the target by i) applying a voltage between the discharger and the collector electrode, ii) discharging the material solution of the fibers towards the first surface of the target, iii) shifting the target in a direction parallel to the first surface thereof, and iv) regulating a target distance between the top portion of the collector electrode and the second surface of the target. The fiber assembly produced by the method has the desirable deposited pattern on the target.

[Preparation step] The material solution containing a raw material of the fibers and a target (base member) are prepared. The material solution contains a solvent dissolving the raw material of the fibers.

Although not specifically limited thereto, the raw material of the fibers may be selected appropriately according to the application thereof. Examples of the raw material of the fibers may include, for example, proteins such as collagen, collagen peptide, gelatin, keratin and silk protein; polysaccharide such as pullulan, cellulose, cellophane, starch, chitin, chitosan, alginic acid, corn starch and salts thereof polymers such as polyamide (PA), polyimide (PI), polyamide-imide (PAI), polyetherimide (PEI), polyacetal (POM), polycarbonate (PC), polyetheretherketone (PEEK), polysulfone (PSF), polyethersulfone (PES), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), polyarylate (PAR), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polypropylene (PP), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS). They may be used individually or in combination. The raw material may contain a copolymer of a plurality of monomers constituting those polymers.

Also, although not specifically limited thereto, the solvent may be selected appropriately according to the raw material of the fibers, including, for example, water; alcohol such as methanol, ethanol, 1-propanol, 2-propanol, isobutyl alcohol, hexafluoroisopropanol, tetraethylene glycol, triethylene glycol, dibenzyl alcohol; 1,3-dioxolane, 1,4-dioxane, methyl ethyl ketone, methyl isobutyl ketone, methyl-n-hexyl ketone, methyl-n-propyl ketone, diisopropyl ketone, diisobutyl ketone, acetone, hexafluoroacetone, phenol, formic acid, methyl formate, ethyl formate, propyl formate, methyl benzoate, ethyl benzoate, propyl benzoate, methyl acetate, ethyl acetate, propyl acetate, dimethyl phthalate, diethyl phthalate, dipropyl phthalate, methyl chloride, ethyl chloride, methylene chloride, chloroform, o-chlorotoluene, p-chlorotoluene, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, trichloroethane, dichloropropane, dibromoethane, dibromopropane, methyl bromide, ethyl bromide, propyl bromide, acetic acid, benzene, toluene, hexane, cyclohexane, cyclohexanone, cyclopentane, o-xylene, p-xylene, m-xylene, acetonitrile, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethyl acetamide, dimethyl sulfoxide, and pyridine. The solvent may be utilized alone or one or more solvents may be used in combination thereof.

A mixing ratio of the raw material of the fibers over the solvent in the material solution depends on selected one of the raw material of the fiber and the solvent. The mixing ratio of the raw material of the fibers over the solvent in the material solution may be, for example, in a range between 60 mass % and 98 mass %.

A viscosity of the material solution may be selected appropriately for discharging the material solution in the electrospinning space applied with the electric field. In particular, the viscosity of the material solution measured by a rotating viscometer at a shearing speed of 1/second under the temperature of 25 deg. C may be, for example, in a range of 0.1-30 Pa·s, and preferably in a range of 0.5-30 Pa·s. The viscosity of the material solution within this range allows the electrospinning process in a reliable manner.

The target 20 may have any size and configuration and may be formed of any material selected appropriately in accordance with the application thereof. When the holder 3 is designed to hold a peripheral edge of the target 20, it is preferable that the whole peripheral edges are defined and held by the holder 3 without forming an opening between the holder 3 and the target 20. Also, the target 20 may have any size and configuration, and for example, in a shape of a rectangle having a member of a length in a range between 3 cm and 50 cm, a circle having a diameter in a range between 3 cm and 50 cm, or any irregular shape having the maximum member of a length in a range between 3 cm and 50 cm.

The target 20 may be formed of any material selected appropriately in accordance with the application thereof. Also, the target 20 may have any configuration including, for example, a fiber structure (such as textile, knit fabric, and non-woven fabric), a film, and a porous sheet body (such as a sponge).

When the target 20 is formed as the fiber structure, it may be formed of a material including, for example, glass fiber, cellulose, acrylic resin, polypropylene (PP), polyethylene (PE), PET, polybutylene terephthalate, polyamide (PA), or the combination thereof.

The target 20 in a form of the fiber structure (fiber target) may have a thickness in a range, for example, between 50 μm and 500 μm, and preferably between 150 μm and 400 μm.

The target 20 in a form of the film or porous sheet (film target) may be made of a biocompatible polymer, for example. The biocompatible film target is appropriate for application in contact with a flesh or skin The film target may have a good gas permeability and biodegradablility as well as the biocompatibility. A cosmetic sheet produced by depositing the fibers containing proteins on the film target having the biocompatibility is suitable as a skin patch sheet having cosmetic effects to the skin. The fibers having cosmetic effects may be deposited on the film target 20 selectively on the areas in the cosmetic sheet corresponding to tails of eyes or lines around a mouth.

The fibers of the biocompatible film target may include, for example, proteins, polysaccharide, polyglycolic acid, polylactic acid, polycaprolactone, polyethylene (PE), polyethylene succinate, polyethylene terephthalate (PET), polyethylene glycol, polypropylene glycol, polyglutamic acid or salts thereof, polyvinyl alcohol (PVA), polyurethane (PU), polyanhydride, or a mixture thereof. The biocompatible polymers may be copolymer of a plurality of monomers constituting these polymers.

The film target 20 (or the porous sheet target) may have a thickness of at least 50 nm or preferably at least 100 nm, for easy handling thereof. On the other hand, the thickness of the film target 20 may be not greater than 500 μm, and preferably not greater than 100 μm, for secure contact with the skin. Also, for achieving the good gas permeability, the thickness of the film target 20 may preferably not greater than 10 μm, and more preferably not greater than 1000 nm.

[Arranging Step] The holder 3 along with the target 20 is arranged between the discharger 1 and the collector electrode 2 with the first surface 20 a of the target 20 opposed to the discharger 1. The target 20 may be held and surrounded by the holder 3 shaped in a frame at a given position thereof, which allows the target 20 are kept unloosened, and preferably tightly tensioned. The target 20 may be adhered on the holder 1 by means of an adhesive.

[Electrospinning Step] A voltage is applied between the discharger 1 and the collector electrode 2 while discharging the material solution from the discharger 1 thereby electrospinning and depositing the fibers on the first surface 20X of the target 20. The collector electrode 2 includes the base portion 2B and the top portion 2T as described above.

In the electrospinning step, the shift regulator 13 shifts the holder 3 in the direction parallel to the first surface 20X of the target 20, and the distance regulator 14 (e.g., the first or second elevator) regulates the distance A between the top portion 2T of the collector electrode 2 and the second surface 20Y of the target 20 so as to form the fiber assembly having a given deposited condition thereon.

The step for shifting the holder 3 may be achieved simultaneously with the step for regulating the distance A. Preferably, the step for shifting the holder 3 may be performed at a timing different from the step for regulating the distance A so as to improve the accuracy of the deposited pattern. The step for shifting the holder 3 and the step for regulating the distance A may be achieved while discharging the material solution from the discharger 1. It should be noted that the distance regulator 14 can regulate whether or not the fiber is deposited on the target 20 by controlling the distance A. In other words, the distance regulator 14 is used to perform a function of a switch for depositing the fibers onto the target 20, through the regulation of the distance A.

In the step for changing the distance A, the distance regulator 14 (the first elevator) regulates the distance A by moving the collector electrode 2 upward or downward relative to the target 20, while the first direction extending from the discharger 1 to the top portion 2T is kept unchanged. Alternatively, in the step for changing the distance A, the distance regulator 14 (the second elevator) regulates the distance A by moving the target 20 upward or downward relative to the collector electrode 2. Meantime, in the step for shifting the holder 3, the shift regulator 13 may preferably shift the holder 3 while maintaining the distance A stationary.

Although not specifically limited thereto, an average diameter of the fiber to be deposited may be determined in accordance with the application of the target 20 with the fiber assembly. For example, the average diameter of the fiber may be at least 50 nm and no greater than 3 μm. In particular when used as the biocompatible sheet on the skin, the average diameter of the fiber may be preferably not greater than 600 μm, more preferably not greater than 200 μm, even more preferably not greater than 100 μm. This is because the thinner sheet causes the closer contact with the skin.

The average fiber diameter is referred to as a mean value of those of the various fibers. The diameter of the fiber is typically that of the cross section taken along a plane perpendicular to the longitudinal direction thereof. However, when the cross section is not circular, the diameter of the fiber may be regarded as the maximum diameter of the fiber. Alternatively, the diameter of the fiber may be referred to as the width thereof in a direction perpendicular to the longitudinal direction thereof, when viewed from the Z-direction (a direction perpendicular to the first surface of the target 20). The average fiber diameter of any number (for example, ten) of the fibers forming the fiber assembly is an averaged diameter of those fibers.

The electrospinning step may be repeated several times with different types/kinds of the top portions 2T and material solutions, as required. After the electrospinning step, the solvents contained in the fiber assembly may be removed, by blowing an air, depressurizing, or heating without damaging the fiber assembly.

FIG. 7 is a photograph of the fiber assembly produced by means of the electrospinning apparatus and the production method according to the present embodiment. The fiber assemblies having desired patterns (alphabets “P S F S” which is abbreviated for Panasonic Smart Factory Solution) were deposited on the film target 20 with use of the collector electrode 2 having the hemispherical top portion 2T (5 mm of the curvature radius) as shown in FIG. 5A and in contact with the target 20 (that is, the distance A is 0 mm). The fibers were formed of polyvinylidene fluoride (PVDF), and each of the alphabets has the width of 0.3 mm.

As described above, according to the present embodiments of the present invention, the electrospinning apparatus and the production method of the fiber assembly can be used in various applications to deposit the fibers at any positions or desired pattern on the target.

REFERENCE NUMERALS

1: discharger, 1A: first flow channel, 1 a: first discharging outlet, 1B: second flow channel, 1 b: second discharging outlet, 2, 2A-2G: collector electrode, 2B, 2Ba-2Bg: base portion 2T, 2Ta-2Tg: top portion, 21Tf, 21Tg: cone, 22Tf: prismatic column, 23Tg: ring, 3: holder, 10: electrospinning apparatus, 11: controller, 12: power supply, 13: shift regulator, 14: distance regulator, 15: human/machine interface (HMI), 16: deposited-condition detector, 17: distance detector, 20: target (base member), 20X: first surface, 20 a: deposition region, 20 b: non-deposition region, 20Y: second surface, 30: material solution 

What is claimed is:
 1. An electrospinning apparatus for depositing fibers on a target having first and second surfaces opposed to each other, the electrospinning apparatus comprising: a discharger that discharges a material solution of the fibers towards the first surface of the target; a collector electrode containing a base portion and a top portion opposed to the discharger; a holder that holds the target between the discharger and the collector electrode so that the first surface of the target is opposed to the discharger; a power supply that applies a voltage between the discharger and the collector electrode; a shift regulator that shifts the holder in a direction parallel to the first surface of the target; a distance regulator that regulates a target distance between the top portion of the collector electrode and the second surface of the target; and a controller that controls the shift regulator and the distance regulator to produce a fiber assembly having a given deposited condition on the first surface of the target.
 2. The electrospinning apparatus according to claim 1, wherein the distance regulator regulates the target distance by moving the holder.
 3. The electrospinning apparatus according to claim 1, wherein the distance regulator changes the target distance by moving the collector electrode.
 4. The electrospinning apparatus according to claim 1, wherein a first direction extending from the discharger to the top portion of the collector electrode is unchanged, while the material solution is discharged from the discharger.
 5. The electrospinning apparatus according to claim 4, wherein the first direction is inclined to a direction perpendicular to the first surface at an acute angle of 20 degrees or less.
 6. The electrospinning apparatus according to claim 1, wherein the shift regulator shifts the holder while maintaining the target distance unchanged.
 7. The electrospinning apparatus according to claim 1, wherein the first surface of the target has a deposition section allowing the fiber to be deposited and a non-deposition section surrounding the deposition section, and wherein the holder holds the target at least partially with either one of the non-deposition section on the first surface and a section on the second surface that is opposed to the non-deposition section on the first surface.
 8. The electrospinning apparatus according to claim 1, wherein the discharger defines a first flow channel for guiding the material solution to a first discharging outlet for discharging the material solution therefrom towards the target, and a second flow channel isolated from the first flow channel for guiding a gas to a second flow channel for discharging the gas therefrom towards the target, and wherein the second discharging outlet is defined so as to surround the first discharging outlet or the first flow channel.
 9. A method for producing a fiber assembly, comprising steps of: preparing a material solution containing a raw material of fibers; preparing a target having first and second surfaces opposed to each other; holding the target between a discharger and a collector electrode so that the first surface of the target is opposed to the discharger, the collector electrode containing a base portion and a top portion opposed to the discharger; electrospinning a fiber to form a fiber assembly having a given deposited condition on the first surface of the target by: i) applying a voltage between the discharger and the collector electrode, ii) discharging the material solution of the fibers towards the first surface of the target, iii) shifting the target in a direction parallel to the first surface thereof, and iv) regulating a target distance between the top portion of the collector electrode and the second surface of the target.
 10. The method for producing the fiber assembly according to claim 9, wherein the target distance is regulated by moving the holder.
 11. The method for producing the fiber assembly according to claim 9, wherein the target distance is regulated by moving the collector electrode.
 12. The method for producing the fiber assembly according claim 9, wherein a first direction extending from the discharger to the top portion of the collector electrode is unchanged, while the material solution is discharged from the discharger.
 13. The method for producing the fiber assembly according to claim 12, wherein the first direction is inclined to a direction perpendicular to the first surface at an acute angle of 20 degrees or less.
 14. The method for producing the fiber assembly according claim 9, wherein a holder holding the target is shifted while maintaining the target distance unchanged.
 15. The method for producing the fiber assembly according to claim 9, wherein wherein the first surface of the target has a deposition section allowing the fiber to be deposited and a non-deposition section surrounding the deposition section, and wherein a holder holds the target at least partially with either one of the non-deposition section on the first surface and a section on the second surface that is opposed to the non-deposition section on the first surface. 